A known capacitor insulated low-capacity power supply is configured to rectify and smooth an AC voltage applied to first and second capacitors, to use the rectified and smoothed voltage as power supply in a power saving mode of an image forming apparatus.
When one of the capacitors experiences a short circuit failure, a higher voltage than desired may possibly be applied from the AC power supply side to the DC output side (load side). Therefore, countermeasures are required to ensure safety of the image forming apparatus when the capacitor has a short circuit failure.